Skin covers the entire bodies of various animals, including humans, and is exposed to the formation of wrinkles, hardening, age spots, darkening and decreased elasticity and the like caused by aging and external factors such as sunlight, dryness, oxidation, environmental stress and psychological stress.
Natural skin is broadly composed of two layers consisting of the epidermis and the dermis, and a thin, minute membrane referred to as the epidermal basement membrane is present between the epidermis and dermis. The epidermal basement membrane is an extremely thin structure having a thickness of about 0.1 μm, and is present in the form of a sheet at the junction between the epidermis and dermis. In addition to the epidermal basement membrane having a basic structure comprised of the lamina densa and lamina lucida, it is also composed of keratinocyte hemidesmosomes, anchoring fragments, anchoring fibers and the like, and in particular, the basic structure thereof is composed of, for example, type IV collagen and various types of laminins and proteoglycans. The main component of epidermal basal cells and the basic structure, and particularly the anchoring fragments bound to the lamina densa, is laminin-5, and the basic structure and dermal collagen fibers are connected by anchoring fibers composed mainly of type VII collagen. In addition, the anchoring fragments and anchoring fibers are mutually bound, and form complexes referred to as anchoring complexes. As a result of having such a structure, the skin, which is present on the outermost layer of the body, maintains a degree of strength capable of withstanding external mechanical stress (Encyclopedia of Cosmetics, Society of Cosmetic Chemists of Japan, pp. 405-406).
However, there is a growing demand for artificial skin to be used as a substitute in the case original skin (namely, natural skin) has become damaged for some reason. In addition, it is also extremely important to develop artificial skin for use as an experimental material for testing the action of pharmaceuticals and cosmetics on the skin, and in either of these applications, there is a strong desire for artificial skin that mimics the structure of natural skin as closely as possible.
A known method for producing artificial skin of the prior art consists of culturing normal human epidermal keratinocytes on a shrunken collagen gel containing human fibroblasts to form an epidermal layer. However, in this method, since a basement membrane is not adequately formed between the collagen gel that mimics the dermis and the epidermal layer that mimics the epidermis, in the case of using this artificial skin, reformation of skin basement membrane was promoted by the administration of a matrix metalloproteinase or both a matrix metalloproteinase and a matrix protein production promoter (Japanese Unexamined Patent Publication No. 2001-269398). In addition, substances that inhibit serine proteases, type IV or type VII collagen, which is the main constituent of the epidermal basement membrane, or substances that enhance the production output of laminin-5 are known to promote the basement membrane formation promoting effects of matrix metalloproteinase inhibitors (Japanese Unexamined Patent Publication No. 2004-75661). However, in the case of this artificial skin produced according to the prior art, the formation of higher-order structures of the epidermal basement membrane and the dermis remains undeveloped, thereby preventing adequate communication between the epidermal basement membrane and the dermis.
In addition, although compounds that inhibit heparanase are known to improve basement membrane function in the body and thereby inhibit the formation of wrinkles in the process by which wrinkles are formed in the skin (International Publication No. WO 2009/123215), the combination of these compounds with a matrix metalloproteinase inhibitor is not known to promote the reformation of epidermal basement membrane and dermis in artificial skin.